I've had the same thing happen with the baseball and football. The items are still usable, but they can't be removed from that sim's inventory at all. Also, if that sim dies, another sim will inherit the item and won't be able to get rid of it either. I've also heard of this happening with cars, gems, guitars, and of course, teddy bears.
It is said that deleting the cache files can fix this. I've never been able to test this, however, as the game my problem happened in got corrupted long before I even knew about the existence of cache files.